rear speaker question

[Speed3driver]

Hey guys, Im not a hardcore audio guy, but I do like having nice equipment and do hear the difference. I used to be a HTIB guy, and changed that a while ago with when I bought a pioneer receiver and a the polk audio RM6750 speaker package about 2 years ago. I am starting to replace my speakers, started out with the front L/R switching to the Infinity P362's which I am very happy with. My birthday is on Friday, so my wife is getting me the Infinity PC-350 center channel speaker. So that leaves me the somewhat weak 8" polk sub(which I will be later swapping out) and the polk satellinte rears. I recently went to Fry's and due to not being able to pass up a great deal, they had the Yamaha NS225's on clearance from $199ea down to $49ea. So I bought a pair and plan on using for the new rears. Here is my dilemma, I think the polks do fine for the rear, and am thinking of posting the yamahas on craigslist or seling them to buy the upgraded sub. Or do you think the benefits of them as rear speakers would be worth keeping them. The sub sounds decent, but I know there is much better out there. What do you thing, could use some help deciding here.

Thanks guys,

Daniel in Seattle